SQL & PL/SQL

Hi,

First query returns rows but not 2nd, please advise why it happened.

SELECT SUM (DECODE (session_state, 'ON CPU', 1, 0) ) oncpu

     , SUM (DECODE (session_state, 'WAITING', 1, 0) ) waiting

FROM v$active_session_history

WHERE sample_time >= SYSDATE - 3 / 24 / 60;

SELECT SUM (DECODE (session_state, 'ON CPU', 1, 0) ) oncpu

     , SUM (DECODE (session_state, 'WAITING', 1, 0) ) waiting

FROM v$active_session_history

WHERE sample_time >= systimestamp - INTERVAL '3' MINUTE;